1. Field of the Invention
The present invention relates to antennas. More specifically the present invention relates to focal plane array antennas.
While the invention is described herein with reference to a particular embodiment for an illustrative application, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teaching provided herein will recognize additional modifications, applications and embodiments within the scope thereof.
2. Description of the Related Art
Focal plane array antennas include an array of radiating elements which may be individually excited to provide an electronically steered beam. Microstrip patch antenna arrays provide a focal plane array antenna of lightweight construction which is particularly useful for spacecraft applications. A conventional microstrip patch antenna includes an array of conductive patch radiating elements mounted on a dielectric substrate. The radiating elements are typically fed by a transmission line. The transmission line typically runs on the element surface of the dielectric substrate and is solder connected to an input connector. The input connector extends through the dielectric substrate and facilitates communication with associated circuitry.
Unfortunately, conventional microstrip patch focal plane array antennas have certain limitations. First, the surface mounted transmission line, precludes the close spacing of the radiating elements. The inability to closely space the radiating elements increases the weight and cost of the antenna, making it less desirable for certain applications, e.g. spacecraft.
Secondly, the direct electrical connection of the radiating elements to the processing circuits provides a conductor for thermal energy. The microstrip radiators act as solar heat collectors and generate a thermal load which may be communicated to the somewhat sensitive processing circuits. Thus, the cost associated with conventional patch antennas is typically increased by the need for thermal protection to guard against such damage.
The article "Aperture Coupled Patch Antennas and Arrays" by Daniel H. Schaubert and David M. Pozar, published by the Department of Electrical Engineering and Computer Engineering University of Massachusetts discloses methods of fabrication to improve performance and reduce the cost per element in large microstrip patch antenna arrays. The technique disclosed involves the use of aperture coupled patch radiators for focal plane array antennas. The aperture coupled patch radiator consists of a three layer network: a feed substrate, a ground plane with an aperture, and a microstrip patch located on an antenna substrate. As energy is coupled to the microstrip feedline, it is directed towards the ground plane. The coupled energy is received by the patch radiator through an electrically small aperture in the ground plane. The energy is then reradiated by the microstrip patch radiator. Electrical connections are supposedly not required and performance is ostensibly insensitive to misalignment of the two circuits. However, this coupling approach requires an additional substrate board, which increases the weight and cost per unit of the focal plane array antenna.
There is therefore a need in the art for a wide bandwidth microstrip patch antenna array having radiating elements closely spaced and thermally isolated from associated electronics.